Conventional thermo-transfer recording medium are comprised of a substrate sheet having thermosensitive solid ink disposed thereon. Although two or more different kinds of ink may be disposed on the substrate sheet, all the inks have the same melting point. Accordingly, the medium prepared cannot be utilized to obtain an intermediate tone by a process which applies a single temperature over a given area.
Recently, other thermorecording medium have been developed which are utilized to place an image on a recording sheet having different tones. The thermal medium includes a support and heat-sensitive ink spots different in tone from one another placed on different spots of the substrate. However, each of the heat-sensitive ink spots is comprised of an ink having the same melting point. Accordingly, it is not possible to utilize the application of different temperatures to obtain different tones on the recording sheet. Furthermore, it is not possible to obtain any given number of different tones at any particular point on the recording sheet.
In order to utilize a thermorecording medium as referred to above having inks of different tones positioned on the substrate, a particular type of heat-generating element must be utilized. In order to obtain the different tones available from the different spots of ink placed on the substrate, the heat-generating head must be precisely constructed and aligned so that heat can be applied to particular spots on the medium which are necessary to create the desired tone.
By placing different colored ink on different places on the substrate, a multi-colored image can be placed on the recording sheet. However, the heat-generating elements of the heat-generating head as well as the electrical leads in connection therewith must be precisely aligned and positioned depending upon the position of the different colored ink on the substrate. Accordingly, the construction of such a heat-generating element as well as its operation is delicate and intricate and therefore expensive.